Glucocorticoid repression of pro-opiomelanocortin gene transcription

Transcription of the pro-opiomelanocortin (POMC) gene is repressed by glucocorticoids in the anterior pituitary gland. We have defined an element within the POMC promoter which is responsible for this regulatory feedback. This element, the "negative glucocorticoid response element" (nGRE), was localized in the proximal region of the POMC promoter and it contains a binding site for the glucocorticoid receptor. Receptor binding to the nGRE was correlated to hormone-dependent repression by using promoter mutagenesis. The nGRE was also shown to contain a binding site for a nuclear protein of the COUP family of transcription factors. Since the binding sites for COUP and the glucocorticoid receptor overlap, glucocorticoid-dependent repression of POMC transcription may result from mutually exclusive binding of these two nuclear transcription factors.

High-resolution mapping of DNase I hypersensitive site in the chicken beta-tubulin gene transfected into monkey cells

In this report, we describe a method for high-resolution mapping of a nuclease hypersensitive site (HS) at the promoter region of the chicken beta 2-tubulin gene transfected into monkey Cos-7 cells. Using the indirect end-labeling method of Wu, a tissue-specific nuclease HS was located initially approximately 100 base pairs upstream of the transcription start site. For high-resolution mapping of the HS in the transfected DNA, a DNA fragment of about 400 base pairs containing the promoter region of the beta 2 gene was subcloned into M13 phage. A single-stranded DNA probe with a defined restriction enzyme cleavage site at one end was prepared from the M13 phage DNA template. The single-stranded probe and the restriction enzyme-digested DNA, prepared from nuclease-digested nuclei from transfected cells, were sequentially annealed back to the template. After ligation between the probe and the transfected DNA, the HS was determined by DNA sequencing gel electrophoresis. This method permits determination of the 3' boundary of the HS with precision at the single-nucleotide level. We mapped a major HS at -107 nucleotides of the beta 2-tubulin gene, where a CACCC-like sequence is present. The application of this method in determining HS is discussed.

Digestion of the chicken beta-globin gene chromatin with micrococcal nuclease reveals the presence of an altered nucleosomal array characterized by an atypical ladder of DNA fragments

The structure of the chicken adult beta-globin gene chromatin in immature and mature erythrocyte nuclei has been analysed using micrococcal nuclease digestion. The resulting DNA fragments were blotted onto DBM-papers and probed with labelled DNA fragments spanning the adult beta-globin gene and its 5'- and 3'-flanking regions. The structure of the nucleosomes within and in the regions flanking the adult beta-globin gene appears to be altered in at least two ways in erythrocyte chromatin, when compared with either bulk or inactive ovalbumin gene chromatin. First, oligomeric DNA fragments containing the beta-globin gene are released faster than those of either bulk or ovalbumin gene chromatin. Second, although the difference in size of the liberated oligomeric DNA fragments is similar to the nucleosomal repeat length of bulk and ovalbumin gene chromatin, the individual oligomers are approximately 100 bp shorter than their bulk or ovalbumin gene counterparts, most noticeably when the nuclease digestion is performed at 37 degrees C. This results in an atypical ladder of approximately 300, 500, 700, 900 bp instead of the canonical chicken erythrocyte ladder which is an integral multiple of 207 bp. The same ladder was obtained from immature erythrocytes, in which the beta-globin gene is actively transcribed, and from mature erythrocytes, in which it is considered to be inactive with RNA polymerase molecules clustered in the 5' moiety of the gene. This indicates that the alteration of the nucleosomal structure is not due to transcription per se.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple and efficient method for the separation and detection of small DNA fragments by electrophoresis in formamide containing agarose gels and Southern blotting to DBM-paper

We show in this report that DNA fragments smaller than 300 bp are separated with high resolution by electrophoresis in concentrated (up to 7%) agarose gels containing 50% formamide. The separated DNA fragments can subsequently be quantitatively transferred to DBM-paper [Alwine, J.C. et al., Proc. Natl. Acad. Sci. USA (1977) 74, 5350-54] using the Southern technique [Southern, E.M., J. Mol. Biol. (1975) 98, 503-517], while preserving the sharpness of the original gel pattern. Since thin (0.2-0.4 mm) and thick (up to 5 mm) agarose slab gels can be easily handled in vertical or horizontal apparatus, this method should prove to be a very useful extention of the Southern technique, applicable to a variety of analytical and preparative purposes.

Characteristics of invasiveness of human nasopharyngeal carcinoma cells in organ culture, as observed by scanning electron microscopy

Cells of a human nasopharyngeal carcinoma (CNE) were cultured in contact with embryonal mouse heart fragments wrapped in a fibrous kidney capsule as biological permeable membrane. The culture was terminated at different intervals and processed for scanning electron microscopy. Carcinoma cells showed abundant microvilli and filopodia in contact with superficial cells of the heart fragments. Cancer cells appeared firmly attached to the surface of the tissue fragments. Subsequently, malignant cells extended pseudopodia into intercellular spaces of the supporting tissue particle, and beyond the third day of cultivation, cancer cells were also found in deeper parts of the organ. The cancer cells on the surface of the specimen had apparently lost the ability to invade. After a while, microvilli and filopodia decreased in number or adhered to each other. The plasma membrane exhibited signs of degeneration.

Submegahertz frequency-stabilized Nd:YAG oscillator

We have demonstrated a 5-msec, quasi-cw 10-Hz repetition-rate pulsed single-frequency Nd:YAG oscillator with a feedback-stabilized frequency bandwidth of less than 200 kHz.